1. Field of the Invention
The present invention relates to an apparatus for the storage and the controlled deliver of products under pressure. This apparatus, compared with conventional spray cans, makes it possible to use either a reduced quantity of liquid gas or else compressed gases as the propelling force.
2. Description of the Prior Art
The ban on halogenated hydrocarbons, known under the names of FRIGEN or FREON, has led to the extensive use of hydrocarbons such as propane and butane, or dimethylether and mixtures of these. Both FRIGEN and FREON are hazardous for the ozone layer that surrounds the earth, and butane and propane, as well as dimethylether, are dangerous for the filling industry because of their explosive characteristics, as well as for the user, since deaths have been caused by the explosion of these substances.
In addition to these flammable gases, it is known that non-inflammable, only partially halogenated FREON 22 (chemical formula CHClF.sub.2) can be used as a propellant. This can also be used in the USA and in the Scandinavian countries, where both FREON and FRIGEN are banned, because FREON 22 contains an additional hydrogen atom and, for this reason, is not as persistent as the fully-halogenated hydrocarbons. Since, however, the vapour pressure of the non-inflammable FREON 22 is extremely high and at 20.degree. C. is approximately 9 bar, it must either be mixed with a gas with a lower vapour pressure, such as dimethylether or butane (which are flammable), or else used in reduced quantities, which is to say, between 18-50%-wt, depending on container quality. In particular, its use in glass vessels, without any plastic, for toilet preparations is problematic. This is because a pressure of 1.5 bar at 20.degree. C. must not be exceeded but, depending on the content of water or ether oil, this pressure is reached at a FREON 22 content of 18%-20%. Since, however, the atomizing quality of conventional sprays depends to a great extent on the proportion of liquid gas, and thus on its expansion, the percentage of approximately 20% FREON 22 in place of the normal 50% FREON 114/12 is not sufficient to atomize toilet water such that the size of the droplets is so fine that the spray will be perceived as "not wet."
Metal cans are also subject to pressure limits imposed by law, so that here, too, one has to work with smaller quantities of FREON 22 that are smaller than those used in conventional spray cans.
The search for a solution for the problem described above has lead to a spray nozzle as described in European Patent No. 0000688, which produces extremely fine vaporization by purely mechanical means. In addition, apparatus have been developed as described in European Patent Nos. 0057226 and 0109361, and in PCT-application CH86/00103, published on Jan. 20, 1987 under the number WO87/00513, that permit the use of compressed air instead of liquid gas as the propellant, wherein, despite a diminishing propellant pressure, an almost constant ejection rate per unit time and a steady particle size are achieved.
Both the use of a reduced quantity of liquid gas, of only approximately 20%, or of compressed air, leads to difficulties. The aerosols that are commercially available all permit some leakage of the product after use, despite the fact that the valve has been closed. If such a valve is used with a high (normal) percentage of liquid gas, one cannot detect this leakage, because when in their liquid phase these gases simultaneously serve as solvents mixed with the active product. They are expelled in liquid form when the valve is opened which leads, when in contact with atmospheric pressure, to an explosion-like vaporization of both the liquid gas as well as of the product carrier, such as alcohol or water. If, however, one uses compressed gas such as air or nitrogen as the propellant, or if one uses a lower percentage of liquid gas, e.g. less than 25%, then this rapid-vaporization factor is either absent or else is so small that the violent vaporization that conceals the leakage or after-flow does not take place.
This leakage or after-flow can be attributed to several factors. In the so-called "male" valves, a plunger is provided with side holes which, when the valve is closed, lie within the substance of the rubber seal, so that no product can escape. Since, however, the central hole of the seal is stamped out, it has vertical grooves that are parallel to its axis, the depths of these varying as a function of the quality or amount of wear in the die, and through which the product can leak once the valve has been closed, until such time as the rubber creeps into the side holes of the plunger and closes them off. In so-called "female" valves, the valve is closed off by the annular rib of a plunger penetrating into a rubber gasket. The edge of most annular ribs is 0.4 to 0.5 mm wide, which means that, depending on the hardness of the rubber, the plunger will penetrate into the seal slowly, which can also lead to a leakage through such valves once they have been closed.
Depending on the quality of the valves, up to 0.03 ml can leak out each time the valve is opened. This leakage is not only messy; it can also lead to blockage of the vaporizer nozzles. In the case of hair spray, drying out of the film binders on the nozzle occurs, if the propellant force is generated by a lower percentage of liquid gas or compressed gas. The use of compressed gases or a lower proportion of liquid gas also causes other problems in that, because of a lack of pressure, not all the product can be expelled from the container.
In a spray can that is filled with liquid gas, the pressure is built up once again after every use by the continuing gasification of the liquid phase so that for all practical purposes there is a constant pressure in the can. At a lower percentage of liquid gas the quantity of gas is just sufficient to keep the pressure constant and to expel all the contents from the container. However, if one sprays for too long a period during one valve opening, this gasification leads to a cooling of the can, which then slows down the gasification, which means that not only does the pressure fall but more liquid gas than is intended is expelled and, for this reason there is insufficient to empty the can. Even if the can is used with the spray head underneath, the gas will be lost so that once again there will not be enough of it.
This problem is much more serious when compressed gas is used as a propellant because then the pressure cannot build up again. Depending on the position of the can, all the pressure can be completely lost, so that the remaining contents of the can, which can no longer be expelled, are wasted.
Despite the sealing that is used there can be a loss of pressure between the valve plate and the neck of the can. For example, if aluminum cans are produced by deep-drawing aluminum disks, grooves that are parallel to the axis of the can are formed in the outer wall of the can. Depending on the diameter of the can, these grooves can be between 0.02 and 0.08 mm deep, but are so narrow that the outer rubber seal cannot penetrate into them and thus cannot seal them off. Even though these grooves can be ground out or filled with a coat of lacquer, depending on the type of can that is involved, there is still a loss of pressure if the valve is not installed with the necessary precision.
A loss of pressure in compressed gases caused by holding the can incorrectly can be avoided by using a two-chamber system, in which the product is stored in a flexible inner container and the propellant, compressed gas, is stored in a rigid outer container. The latter acts on the flexible inner container and compresses this, which means that the product contained therein is expelled. Such systems are known. Their flexible inner containers must, however, be installed prior to the attachment of the base of the can or, in the case of monobloc cans, before the shoulder section is rolled. In addition, filling the cans with compressed gas is relatively complicated and demands a high level of precision, which is costly. In this regard, the base of the can may be provided with an opening which can be closed by means of a rubber stopper, the compressed gas is introduced into the can, whereupon the rubber plug is pressed completely into the opening, which it then seals hermetically. In addition to the necessary precision, this charging procedure takes up a great deal of time so that mass production becomes extremely costly.
Metal cans require many times the energy--both for the production of the metal as such and also for the producation of the cans-- than is required to produce plastic, and cans of this material. Corrosion problems may also be encountered, depending on the type of metal that is used.
In order to avoid pressure losses caused by incorrect manipulation of the can when compressed gases are used there are valves on the market which, thanks to a ball, make it possible to spray the product even if the can is held upside down. However, such cans cannot prevent a loss of pressure if the can is held in an inclined position and the riser tube for the valve, because it is nearly always curved, is not in, but out of, the product.